When you bring two bar magnets (of roughly equal strength) together with N facing S, the magnetic field of the second magnet is in the same direction as the magnetization vector (M) in the first magnet. Therefore it tends to increase that magnetization, increasing the attractive force between the magnets. If you bring them together with N facing N, the field in the second magnet opposes the magnetization vector in the first magnet and tends to weaken it. This makes the repulsive force less than the corresponding attractive force.

 

 

Then the amount that it is lessened has to be related to the work done in rotating the magnet 180 degrees in the presence of the other magnet.

Then the amount that it is lessened has to be related to the work done in rotating the magnet 180 degrees in the presence of the other magnet.

Of course, but I just wanted to answer the question asked.

If the two magnets are perfectly aligned lengthwise as they approach each other, from whence comes the rotation which supplies the mechanical energy?

If the two magnets are perfectly aligned lengthwise as they approach each other, from whence comes the rotation which supplies the mechanical energy?

 

Any magnetic dipole will feel a torque in the presence of an external field, unless it is perfectly aligned, which is a point if unstable equilibrium.

Two dipoles, perfectly aligned, neither under the influence of any field except that which they jointly contribute, dont quite see where the destabilising force comes from. But that notwithstanding (unless this situation is the sole answer), I dont sense the approach of a definitive conclusion.

Therefore it tends to increase that magnetization, increasing the attractive force between the magnets

 

Is there a formula for calculating the difference between the repulsion and attraction of two identical magnets?

Is there a formula for calculating the difference between the repulsion and attraction of two identical magnets?

 

Nice question. I thought this thread had died. Have been hunting all over the net for a definitive statement. no success so far.

There is no simple formula because it depends on too many factors: The type of ferromagnetic material, its history, its shape, etc. The point is that the dipole atoms are locked in place by a cooperative mechanism. In the case of repulsion, the opposing field tries to unlock them. The extent to which this happens is different in different cases. Its like what happens to the electorate after a state of the union speech.

I did see a website of a company that sold magnets that did list attraction and repulsion for the magnets they sold. I don't remember its URL.

I think I put "magnets" into google.